U.S. patent number 6,268,239 [Application Number 09/552,797] was granted by the patent office on 2001-07-31 for semiconductor chip cooling structure and manufacturing method thereof.
This patent grant is currently assigned to NEC Corporation. Invention is credited to Renya Ikeda.
United States Patent |
6,268,239 |
Ikeda |
July 31, 2001 |
Semiconductor chip cooling structure and manufacturing method
thereof
Abstract
A semiconductor chip is mounted on a small-size circuit board
having a hole, in flip-chip mounting. The small-size circuit board
is connected to a large-size circuit board so that the
semiconductor chip will be placed between the small-size circuit
board and the large-size circuit board and there will be a
clearance between the semiconductor chip and the large-size circuit
board. A heat sink is provided with a convex part for being
inserted into the hole of the small-size circuit board to be
thermally connected to the surface of the semiconductor chip
through a thermal conduction material which is sandwiched between
the convex part and the semiconductor chip. The heat sink is fixed
to the large-size circuit board by means of fixation screws etc. so
that the semiconductor chip and the small-size circuit board will
be placed between the heat sink and the large-size circuit board.
The fixation load for fixing the heat sink to the large-size
circuit board is not applied to the semiconductor chip at all and
thereby damages to the semiconductor chip due to the fixation is
eliminated. The surface of the semiconductor chip is almost
directly connected to the convex part of the heat sink via the
thermal conduction material, therefore, the cooling of the
semiconductor chip in flip-chip mounting is executed with high
cooling efficiency.
Inventors: |
Ikeda; Renya (Tokyo,
JP) |
Assignee: |
NEC Corporation (Tokyo,
JP)
|
Family
ID: |
14599265 |
Appl.
No.: |
09/552,797 |
Filed: |
April 20, 2000 |
Foreign Application Priority Data
|
|
|
|
|
Apr 20, 1999 [JP] |
|
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11-112938 |
|
Current U.S.
Class: |
438/122; 257/717;
257/719; 257/E23.105; 438/121; 438/125 |
Current CPC
Class: |
H01L
23/3677 (20130101); H05K 1/0204 (20130101); H01L
2224/73253 (20130101); H01L 2924/01079 (20130101); H01L
2924/3011 (20130101); H05K 1/141 (20130101); H05K
3/3436 (20130101); H05K 2201/09054 (20130101); H05K
2201/10477 (20130101); H05K 2201/10674 (20130101); H01L
2224/16225 (20130101); H01L 2224/32245 (20130101); H01L
2224/73203 (20130101); H01L 2924/15151 (20130101); H01L
2924/15321 (20130101) |
Current International
Class: |
H01L
23/367 (20060101); H01L 23/34 (20060101); H05K
1/02 (20060101); H05K 3/34 (20060101); H05K
1/14 (20060101); H01L 021/44 () |
Field of
Search: |
;438/111,121,122,123,124,125,126 ;257/717,718,719,712,713 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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4396936 |
August 1983 |
McIver et al. |
5736785 |
April 1998 |
Chiang et al. |
5814535 |
September 1998 |
Shimada et al. |
5930601 |
July 1999 |
Cannizzaro et al. |
5946544 |
August 1999 |
Estes et al. |
5985697 |
November 1999 |
Chaney et al. |
5999415 |
December 1999 |
Hamzehdoost |
6016006 |
January 2000 |
Kolman et al. |
6020219 |
February 2000 |
Dudderar et al. |
6130113 |
October 2000 |
Eslamy et al. |
|
Foreign Patent Documents
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61-42431 |
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Sep 1986 |
|
JP |
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10-209348 |
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Aug 1998 |
|
JP |
|
Primary Examiner: Picardat; Kevin M.
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A manufacturing method of a semiconductor chip cooling structure
comprising the steps of:
a semiconductor chip mounting step in which a semiconductor chip is
mounted in flip-chip mounting on a small-size circuit board which
has a hole for the semiconductor chip;
a small-size circuit board connection step in which the small-size
circuit board is connected to a large-size circuit board so that
the semiconductor chip will be placed between the small-size
circuit board and the large-size circuit board and there will be a
clearance between the semiconductor chip and the large-size circuit
board; and
a heat sink fixation step in which a heat sink, which is provided
with a convex part for being inserted into the hole of the
small-size circuit board, is fixed to the large-size circuit board
by means of fixation means so that the semiconductor chip and the
small-size circuit board will be placed between the heat sink and
the large-size circuit board and so that the convex part of the
heat sink will be thermally connected to the surface of the
semiconductor chip through a thermal conduction material which is
sandwiched between the convex part and the semiconductor chip.
2. A manufacturing method of a semiconductor chip cooling structure
as claimed in claim 1, wherein a material which is easily deformed
is employed as the thermal conduction material which is sandwiched
between the convex part of the heat sink and the semiconductor
chip.
3. A manufacturing method of a semiconductor chip cooling structure
as claimed in claim 2, wherein the thermal conduction material is
implemented by thermal conduction grease.
4. A manufacturing method of a semiconductor chip cooling structure
as claimed in claim 2, wherein the thermal conduction material is
implemented by a thermal conduction rubber sheet.
5. A manufacturing method of a semiconductor chip cooling structure
as claimed in claim 1, wherein in the heat sink fixation step,
mechanical fixation means such as screws are employed as the
fixation means for fixing the heat sink to the large-size circuit
board.
6. A manufacturing method of a semiconductor chip cooling structure
as claimed in claim 1, wherein in the small-size circuit board
connection step, the small-size circuit board is connected to the
large-size circuit board by means of solder balls each of which
including a copper ball so that enough space can be provided
between the small-size circuit board and the large-size circuit
board.
7. A manufacturing method of a semiconductor chip cooling structure
as claimed in claim 1, further comprising a sealing step in which
the structure between the small-size circuit board and the
large-size circuit board is sealed by a sealing material such as
epoxy resin.
8. A manufacturing method of a semiconductor chip cooling structure
comprising:
a semiconductor chip mounting step in which N (N: 2, 3, 4, . . . )
semiconductor chips are mounted in flip-chip mounting on a
small-size circuit board which has N holes for the N semiconductor
chips;
a small-size circuit board connection step in which the small-size
circuit board is connected to a large-size circuit board so that
the N semiconductor chips will be placed between the small-size
circuit board and the large-size circuit board and there will be
clearances between the N semiconductor chips and the large-size
circuit board; and
a heat sink fixation step in which a heat sink, which is provided
with N convex parts for being inserted into the N holes of the
small-size circuit board respectively, is fixed to the large-size
circuit board by means of fixation means so that the semiconductor
chip and the small-size circuit board will be placed between the
heat sink and the large-size circuit board and so that each convex
part of the heat sink will be thermally connected to the surface of
a corresponding semiconductor chip through a thermal conduction
material which is sandwiched between the convex part and the
semiconductor chip.
9. A manufacturing method of a semiconductor chip cooling structure
as claimed in claim 8, wherein materials which are easily deformed
are employed as the thermal conduction materials which are
sandwiched between the N convex parts of the heat sink and the N
semiconductor chips.
10. A manufacturing method of a semiconductor chip cooling
structure as claimed in claim 9, wherein the thermal conduction
material is implemented by thermal conduction grease.
11. A manufacturing method of a semiconductor chip cooling
structure as claimed in claim 9, wherein the thermal conduction
material is implemented by a thermal conduction rubber sheet.
12. A manufacturing method of a semiconductor chip cooling
structure as claimed in claim 8, wherein in the heat sink fixation
step, mechanical fixation means such as screws are employed as the
fixation means for fixing the heat sink to the large-size circuit
board.
13. A manufacturing method of a semiconductor chip cooling
structure as claimed in claim 8, wherein in the small-size circuit
board connection step, the small-size circuit board is connected to
the large-size circuit board by means of solder balls each of which
including a copper ball so that enough space can be provided
between the small-size circuit board and the large-size circuit
board.
14. A manufacturing method of a semiconductor chip cooling
structure as claimed in claim 8, further comprising a sealing step
in which the structure between the small-size circuit board and the
large-size circuit board is sealed by a sealing material such as
epoxy resin.
15. A semiconductor chip cooling structure comprising:
a semiconductor chip;
a small-size circuit board having a hole, on which the
semiconductor chip is mounted in flip-chip mounting;
a large-size circuit board to which the small-size circuit board is
connected so that the semiconductor chip will be placed between the
small-size circuit board and the large-size circuit board and there
will be a clearance between the semiconductor chip and the
large-size circuit board; and
a heat sink, which is provided with a convex part for being
inserted into the hole of the small-size circuit board to be
thermally connected to the surface of the semiconductor chip
through a thermal conduction material which is sandwiched between
the convex part and the semiconductor chip, and which is fixed to
the large-size circuit board by means of fixation means so that the
semiconductor chip and the small-size circuit board will be placed
between the heat sink and the large-size circuit board.
16. A semiconductor chip cooling structure as claimed in claim 15,
wherein a material which is easily deformed is employed as the
thermal conduction material which is sandwiched between the convex
part of the heat sink and the semiconductor chip.
17. A semiconductor chip cooling structure as claimed in claim 16,
wherein the thermal conduction material is implemented by thermal
conduction grease.
18. A semiconductor chip cooling structure as claimed in claim 16,
wherein the thermal conduction material is implemented by a thermal
conduction rubber sheet.
19. A semiconductor chip cooling structure as claimed in claim 15,
wherein mechanical fixation means such as screws are employed as
the fixation means for fixing the heat sink to the large-size
circuit board.
20. A semiconductor chip cooling structure as claimed in claim 15,
wherein the small-size circuit board is connected to the large-size
circuit board by means of solder balls each of which including a
copper ball so that enough space can be provided between the
small-size circuit board and the large-size circuit board.
21. A semiconductor chip cooling structure as claimed in claim 15,
wherein the structure between the small-size circuit board and the
large-size circuit board is sealed by a sealing material such as
epoxy resin.
22. A semiconductor chip cooling structure comprising:
N (N: 2, 3, 4, . . . ) semiconductor chips;
a small-size circuit board having N holes corresponding to the N
semiconductor chips, on which the N semiconductor chips are mounted
in flip-chip mounting;
a large-size circuit board to which the small-size circuit board is
connected so that the N semiconductor chips will be placed between
the small-size circuit board and the large-size circuit board and
there will be clearances between the N semiconductor chips and the
large-size circuit board; and
a heat sink, which is provided with N convex parts for being
inserted into the N holes of the small-size circuit board
respectively so that each convex part will be thermally connected
to the surface of a corresponding semiconductor chip through a
thermal conduction material which is sandwiched between the convex
part and the semiconductor chip, and which is fixed to the
large-size circuit board by means of fixation means so that the N
semiconductor chips and the small-size circuit board will be placed
between the heat sink and the large-size circuit board.
23. A semiconductor chip cooling structure as claimed in claim 22,
wherein materials which are easily deformed are employed as the
thermal conduction materials which are sandwiched between the N
convex parts of the heat sink and the N semiconductor chips.
24. A semiconductor chip cooling structure as claimed in claim 23,
wherein the thermal conduction material is implemented by thermal
conduction grease.
25. A semiconductor chip cooling structure as claimed in claim 23,
wherein the thermal conduction material is implemented by a thermal
conduction rubber sheet.
26. A semiconductor chip cooling structure as claimed in claim 22,
wherein mechanical fixation means such as screws are employed as
the fixation means for fixing the heat sink to the large-size
circuit board.
27. A semiconductor chip cooling structure as claimed in claim 22,
wherein the small-size circuit board is connected to the large-size
circuit board by means of solder balls each of which including a
copper ball so that enough space can be provided between the
small-size circuit board and the large-size circuit board.
28. A semiconductor chip cooling structure as claimed in claim 22,
wherein the structure between the small-size circuit board and the
large-size circuit board is sealed by a sealing material such as
epoxy resin.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor chip cooling
structure and a manufacturing method of a semiconductor chip
cooling structure, and in particular, to a semiconductor chip
cooling structure and a manufacturing method of a semiconductor
chip cooling structure for a semiconductor chip which is mounted on
a circuit board in "flip-chip" mounting.
DESCRIPTION OF THE PRIOR ART
A semiconductor chip cooling structure, that is, a structure for
letting a semiconductor chip release its heat and thereby cooling
the semiconductor chip, has generally been implemented by use of a
heat sink and a thermal conduction material such as a rubber sheet.
FIG. 1 is a cross sectional view showing an example of a
conventional semiconductor chip cooling structure. Referring to
FIG. 1, a semiconductor chip (in "flip-chip" mounting) is mounted
on a circuit board by means of solder balls etc. so that its
surface will face downward onto the circuit board. A thermal
conduction material such as a rubber sheet is attached to the back
side of the semiconductor chip, and a heat sink is attached to the
back of the thermal conduction material. The heat sink is fixed to
the circuit board by means of fixation screws (bolts and nuts) etc.
so as not to drop from the semiconductor chip and the circuit
board.
In a "Semiconductor Package Structure for Promoting Heat Emission
Effect" which has been disclosed in Japanese Patent Application
Laid-Open No.HEI10-209348 (hereafter, referred to as a "second
conventional semiconductor chip cooling structure"), a
semiconductor chip is mounted on a circuit board so that its
surface will face upward, and a heat emission piece is attached to
the surface of the semiconductor chip, not to the back of the
semiconductor chip. The heat emission piece is implemented by, for
example, a metal plate which is substantially square. To the
surface of the heat emission piece, convexity, concavity, holes,
etc. are provided for some purposes including the prevention of
damages to the surface of the semiconductor chip or bonding wires
when the heat emission piece is attached. By such a structure, the
heat of the semiconductor chip can be released not only from its
back side but also from its upper surface, and thereby the heat
emission effect is improved considerably.
In a "cooling structure for an integrated circuit package" which
has been disclosed in Japanese Publication of Examined Patent
Applications No.SHO61-42431 (hereafter, referred to as a "third
conventional semiconductor chip cooling structure"), a heat sink is
attached to a heat sink pad which has been formed on the back of a
circuit board, and an IC chip is mounted on the surface of the
circuit board in "flip-chip" mounting. Heat conduction channels are
provided to the circuit board so as to penetrate the circuit board
and thereby thermally connect the active surface of the IC chip and
the heat sink on the back of the circuit board. A material
(plastic, solder, etc.) having a thermoplastic/setting property and
large thermal conductivity is filled in the heat conduction
channels by heating the circuit board so as to lower thermal
impedance between the IC chip and the heat sink. In conventional
flip-chip packages, the active surface of the IC chip faces the
circuit board and thus heat emission from the active surface tended
to be disturbed by the existence of the circuit board and it has
been difficult to successfully release the heat emitted by the IC
chip or semiconductor chip especially when large scale IC chips
emitting large amount of heat are used. The third conventional
semiconductor chip cooling structure has been proposed in order to
resolve the heat problems of the flip-chip packages.
However, the conventional techniques which have been described
above involve the following problems or drawbacks. First, in the
first conventional semiconductor chip cooling structure of FIG. 1,
the heat sink is fixed to the circuit board by means of fixation
screws (bolts and nuts) etc. so as to sandwich the semiconductor
chip of flip-chip mounting. Due to such fixation of the heat sink,
the load for the fixation of the heat sink to the circuit board is
also applied to the semiconductor chip through the thermal
conduction material, and thus damages to the semiconductor chip are
easily caused due to the fixation load. Further, the first
conventional semiconductor chip cooling structure of FIG. 1 cools
the semiconductor chip from its back side. The operations of the
semiconductor chip occur in its diffusion layers, electrodes,
lines, etc. which have been formed on the surface (0.about.a few
.mu.m in depth) of the semiconductor chip, and heat is evolved from
the active surface layer of the semiconductor chip. The thickness
of the semiconductor chip is as large as approximately 400 .mu.m,
and thus it is clear that the cooling from the back side is
inefficient than cooling from the surface.
The second conventional semiconductor chip cooling structure cools
the semiconductor chip from its surface by use of the heat emission
piece (square metal plate etc.). However, the structure can not be
applied to the flip-chip mounting having the advantage in
miniaturization of the whole package.
The third conventional semiconductor chip cooling structure
executes cooling of the semiconductor chip (IC chip) of flip-chip
mounting from its surface. However, the cooling of the flip-chip is
mainly done through the thermally conductive material (plastic,
solder, etc.) which is filled in the heat conduction channels of
the circuit board by heating. Thermal conductivity of the thermally
conductive material (plastic etc.) is generally smaller than that
of the metal heat sink itself and the length of the path of heat
conduction through the thermally conductive plastic is longer than
the thickness of the circuit board, therefore, it is difficult to
attain a high cooling efficiency by the third conventional
semiconductor chip cooling structure. Further, the thermal
conductivity of the thermally conductive material (plastic, solder,
etc.) which is filled in the heat conduction channels by heating is
affected by flowing/setting statuses of the thermally conductive
material in the heat conduction channels. If bubbles, interfaces,
unevenness etc. are formed in the heat conduction channels in the
setting of the thermally conductive material, the thermal
conductivity through the heat conduction channels is easily
deteriorated.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to
provide a semiconductor chip cooling structure and a manufacturing
method of a semiconductor chip cooling structure, by which cooling
of a semiconductor chip mounted on a circuit board in flip-chip
mounting can be executed from its surface with high cooling
efficiency and without causing damages due to the fixation loads
etc. to the semiconductor chip.
In accordance with a first aspect of the present invention, there
is provided a semiconductor chip cooling structure comprising a
semiconductor chip, a small-size circuit board, a large-size
circuit board and a heat sink. The semiconductor chip is mounted on
the small-size circuit board having a hole, in flip-chip mounting.
The small-size circuit board is connected to the large-size circuit
board so that the semiconductor chip will be placed between the
small-size circuit board and the large-size circuit board and there
will be a clearance between the semiconductor chip and the
large-size circuit board. The heat sink is provided with a convex
part for being inserted into the hole of the small-size circuit
board to be thermally connected to the surface of the semiconductor
chip through a thermal conduction material which is sandwiched
between the convex part and the semiconductor chip. The heat sink
is fixed to the large-size circuit board by means of fixation means
so that the semiconductor chip and the small-size circuit board
will be placed between the heat sink and the large-size circuit
board.
In accordance with a second aspect of the present invention, in the
first aspect, a material which is easily deformed is employed as
the thermal conduction material which is sandwiched between the
convex part of the heat sink and the semiconductor chip.
In accordance with a third aspect of the present invention, in the
second aspect, the thermal conduction material is implemented by
thermal conduction grease.
In accordance with a fourth aspect of the present invention, in the
second aspect, the thermal conduction material is implemented by a
thermal conduction rubber sheet.
In accordance with a fifth aspect of the present invention, in the
first aspect, mechanical fixation means such as screws are employed
as the fixation means for fixing the heat sink to the large-size
circuit board.
In accordance with a sixth aspect of the present invention, in the
first aspect, the small-size circuit board is connected to the
large-size circuit board by means of solder balls each of which
including a copper ball so that enough space can be provided
between the small-size circuit board and the large-size circuit
board.
In accordance with a seventh aspect of the present invention, in
the first aspect, the structure between the small-size circuit
board and the large-size circuit board is sealed by a sealing
material such as epoxy resin.
In accordance with an eighth aspect of the present invention, there
is provided a semiconductor chip cooling structure comprising N (N:
2, 3, 4, . . . ) semiconductor chips, a small-size circuit board a
large-size circuit board and a heat sink. The small-size circuit
board has N holes corresponding to the N semiconductor chips. The N
semiconductor chips are mounted on the small-size circuit board in
flip-chip mounting. The small-size circuit board is connected to
the large-size circuit board so that the N semiconductor chips will
be placed between the small-size circuit board and the large-size
circuit board and there will be clearances between the N
semiconductor chips and the large-size circuit board. The heat sink
is provided with N convex parts for being inserted into the N holes
of the small-size circuit board respectively so that each convex
part will be thermally connected to the surface of a corresponding
semiconductor chip through a thermal conduction material which is
sandwiched between the convex part and the semiconductor chip. The
heat sink is fixed to the large-size circuit board by means of
fixation means so that the N semiconductor chips and the small-size
circuit board will be placed between the heat sink and the
large-size circuit board.
In accordance with a ninth aspect of the present invention, in the
eighth aspect, materials which are easily deformed are employed as
the thermal conduction materials which are sandwiched between the N
convex parts of the heat sink and the N semiconductor chips.
In accordance with a tenth aspect of the present invention, in the
ninth aspect, the thermal conduction material is implemented by
thermal conduction grease.
In accordance with an eleventh aspect of the present invention, in
the ninth aspect, the thermal conduction material is implemented by
a thermal conduction rubber sheet.
In accordance with a twelfth aspect of the present invention, in
the eighth aspect, mechanical fixation means such as screws are
employed as the fixation means for fixing the heat sink to the
large-size circuit board.
In accordance with a thirteenth aspect of the present invention, in
the eighth aspect, the small-size circuit board is connected to the
large-size circuit board by means of solder balls each of which
including a copper ball so that enough space can be provided
between the small-size circuit board and the large-size circuit
board.
In accordance with a fourteenth aspect of the present invention, in
the eighth aspect, the structure between the small-size circuit
board and the large-size circuit board is sealed by a sealing
material such as epoxy resin.
In accordance with a fifteenth aspect of the present invention,
there is provided a manufacturing method of a semiconductor chip
cooling structure. The manufacturing method comprises a
semiconductor chip mounting step, a small-size circuit board
connection step, and a heat sink fixation step. In the
semiconductor chip mounting step, a semiconductor chip is mounted
in flip-chip mounting on a small-size circuit board which has a
hole for the semiconductor chip. In the small-size circuit board
connection step, the small-size circuit board is connected to a
large-size circuit board so that the semiconductor chip will be
placed between the small-size circuit board and the large-size
circuit board and there will be a clearance between the
semiconductor chip and the large-size circuit board. In the heat
sink fixation step, a heat sink, which is provided with a convex
part for being inserted into the hole of the small-size circuit
board, is fixed to the large-size circuit board by means of
fixation means so that the semiconductor chip and the small-size
circuit board will be placed between the heat sink and the
large-size circuit board and so that the convex part of the heat
sink will be thermally connected to the surface of the
semiconductor chip through a thermal conduction material which is
sandwiched between the convex part and the semiconductor chip.
In accordance with a sixteenth aspect of the present invention, in
the fifteenth aspect, a material which is easily deformed is
employed as the thermal conduction material which is sandwiched
between the convex part of the heat sink and the semiconductor
chip.
In accordance with a seventeenth aspect of the present invention,
in the sixteenth aspect, the thermal conduction material is
implemented by thermal conduction grease.
In accordance with an eighteenth aspect of the present invention,
in the sixteenth aspect, the thermal conduction material is
implemented by a thermal conduction rubber sheet.
In accordance with a nineteenth aspect of the present invention, in
the heat sink fixation step of the fifteenth aspect, mechanical
fixation means such as screws are employed as the fixation means
for fixing the heat sink to the large-size circuit board.
In accordance with a twentieth aspect of the present invention, in
the small-size circuit board connection step of the fifteenth
aspect, the small-size circuit board is connected to the large-size
circuit board by means of solder balls each of which including a
copper ball so that enough space can be provided between the
small-size circuit board and the large-size circuit board.
In accordance with a twenty-first aspect of the present invention,
in the fifteenth aspect, the manufacturing method further comprises
a sealing step. In the sealing step, the structure between the
small-size circuit board and the large-size circuit board is sealed
by a sealing material such as epoxy resin.
In accordance with a twenty-second aspect of the present invention,
there is provided a manufacturing method of a semiconductor chip
cooling structure. The manufacturing method comprises a
semiconductor chip mounting step, a small-size circuit board
connection step, and a heat sink fixation step. In the
semiconductor chip mounting step, N (N: 2, 3, 4, . . . )
semiconductor chips are mounted in flip-chip mounting on a
small-size circuit board which has N holes for the N semiconductor
chips. In the small-size circuit board connection step, the
small-size circuit board is connected to a large-size circuit board
so that the N semiconductor chips will be placed between the
small-size circuit board and the large-size circuit board and there
will be clearances between the N semiconductor chips and the
large-size circuit board. In the heat sink fixation step, a heat
sink, which is provided with N convex parts for being inserted into
the N holes of the small-size circuit board respectively, is fixed
to the large-size circuit board by means of fixation means so that
the semiconductor chip and the small-size circuit board will be
placed between the heat sink and the large-size circuit board and
so that each convex part of the heat sink will be thermally
connected to the surface of a corresponding semiconductor chip
through a thermal conduction material which is sandwiched between
the convex part and the semiconductor chip.
In accordance with a twenty-third aspect of the present invention,
in the twenty-second aspect, materials which are easily deformed
are employed as the thermal conduction materials which are
sandwiched between the N convex parts of the heat sink and the N
semiconductor chips.
In accordance with a twenty-fourth aspect of the present invention,
in the twenty-third aspect, the thermal conduction material is
implemented by thermal conduction grease.
In accordance with a twenty-fifth aspect of the present invention,
in the twenty-third aspect, the thermal conduction material is
implemented by a thermal conduction rubber sheet.
In accordance with a twenty-sixth aspect of the present invention,
in the heat sink fixation step of the twenty-second aspect,
mechanical fixation means such as screws are employed as the
fixation means for fixing the heat sink to the large-size circuit
board.
In accordance with a twenty-seventh aspect of the present
invention, in the small-size circuit board connection step of the
twenty-second aspect, the small-size circuit board is connected to
the large-size circuit board by means of solder balls each of which
including a copper ball so that enough space can be provided
between the small-size circuit board and the large-size circuit
board.
In accordance with a twenty-eighth aspect of the present invention,
in the twenty-second aspect, the manufacturing method further
comprises a sealing step. In the sealing step, the structure
between the small-size circuit board and the large-size circuit
board is sealed by a sealing material such as epoxy resin.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and features of the present invention will become more
apparent from the consideration of the following detailed
description taken in conjunction with the accompanying drawings, in
which:
FIG. 1 is a cross sectional view showing an example of a
conventional semiconductor chip cooling structure;
FIG. 2 is a cross sectional view showing a semiconductor chip
cooling structure in accordance with a first embodiment of the
present invention; and
FIG. 3 is a cross sectional view showing a semiconductor chip
cooling structure in accordance with a second embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, a description will be given in
detail of preferred embodiments in accordance with the present
invention.
FIG. 2 is a cross sectional view showing a semiconductor chip
cooling structure in accordance with a first embodiment of the
present invention. Referring to FIG. 2, the semiconductor chip
cooling structure of the first embodiment includes a semiconductor
chip 1, a small-size circuit board 2, a large-size circuit board 3,
a heat sink 4, a thermal conduction material 5, solder 6, and
fixation screws (bolts and nuts) 7. The small-size circuit board 2
can be a single layer circuit board or a multilayer circuit board.
The large-size circuit board 3 can also be a single layer circuit
board or a multilayer circuit board. The heat sink 4 for emitting
the heat of the semiconductor chip 1 is formed of aluminium,
copper, etc. The solder 6 is used in the semiconductor chip cooling
structure of FIG. 2 as electrically conductive joints.
The semiconductor chip 1 is mounted on the small-size circuit board
2 with its surface facing downward onto the small-size circuit
board 2. At the center of the small-size circuit board 2, a hole
whose aria is smaller than that of the semiconductor chip 1 is
provided.
The small-size circuit board 2 is mounted on the large-size circuit
board 3 by means of electrically conductive joints such as the
solder 6. At the center of the upper surface of the heat sink 4, a
convex part corresponding to the center hole of the small-size
circuit board 2 is formed. The heat sink 4 is fixed to the
large-size circuit board 3 by fixation means such as the fixation
screws 7. Between the convex part of the heat sink 4 and the
semiconductor chip 1, the thermal conduction material 5 (a thermal
conduction compound, thermal conduction grease, a thermal
conduction rubber sheet, etc.) is filled or sandwiched.
Incidentally, in the example of FIG. 2, no fixation means is
provided between the small-size circuit board 2 and the heat sink
4. The small-size circuit board 2 and the heat sink 4 contact each
other due to the fixation by the fixation screws 7.
In the following, an example of a manufacturing method of the
semiconductor chip cooling structure of FIG. 2 will be explained in
detail.
First, the semiconductor chip 1 is mounted on the small-size
circuit board 2 by connecting (by means of soldering etc.) surface
electrodes of the semiconductor chip 1 and pads of the small-size
circuit board 2 which have preliminarily been formed so as to face
the surface electrodes of the semiconductor chip 1. The small-size
circuit board 2 on which the semiconductor chip 1 has been mounted
is thereafter connected to the large-size circuit board 3 by the
solder 6. By the connection by the solder 6, electrical connection
between the small-size circuit board 2 and the large-size circuit
board 3 is established. At this stage, the semiconductor chip 1,
the small-size circuit board 2 and the large-size circuit board 3
have been connected together as an electrically connected
block.
Meanwhile, on the convex part of the heat sink 4, the thermal
conduction material 5 is previously applied or attached.
Thereafter, the heat sink 4 is attached to the large-size circuit
board 3 by means of the fixation means such as the fixation screws
7. Due to the fixation by means of the fixation screws 7, the heat
sink 4 approaches and thereafter contacts the lower surface of the
small-size circuit board 2. Incidentally, the height of the convex
part of the heat sink 4 and the thickness of the thermal conduction
material 5 have been determined and designed so that thermal
connection between the semiconductor chip 1 and the heat sink 4 can
be secured enough.
The load (pressure) for fixing the heat sink 4 to the large-size
circuit board 3 is held and supported by the small-size circuit
board 2 and the solder 6 connecting the small-size circuit board 2
to the large-size circuit board 3, therefore, the load for the
fixation is not applied to the semiconductor chip 1 at all.
Meanwhile, a load that is applied to the semiconductor chip 1 is
determined by the relationship between two thicknesses: a first
thickness of the convex part of the heat sink 4 and the thermal
conduction material 5 added together and a second thickness of the
small-size circuit board 2 and the chip connection part (between
the semiconductor chip 1 and the small-size circuit board 2) added
together. Therefore, the load applied to the semiconductor chip 1
is determined independently from the load for fixing the heat sink
4 to the large-size circuit board 3. Thus, the load applied to the
semiconductor chip 1 can be controlled and reduced enough by
designing the dimensions of the parts appropriately, and damages to
the semiconductor chip 1 due to the fixation load can be
eliminated. Especially, if the thermal conduction material 5 is
implemented by an easily deformed material or a pressure- absorbing
material such as thermal conduction grease, a thermal conduction
rubber sheet, etc., the effect of the fixation load to the
semiconductor chip 1 can be absorbed and eliminated without the
need of determining a precise thickness of the thermal conduction
material 5.
Further, in the semiconductor chip cooling structure of the above
embodiment, the surface of the semiconductor chip 1 is almost
directly connected to the convex part of the heat sink 4 via the
thermal conduction material 5, therefore, the cooling of the
semiconductor chip 1 can be executed more efficiently in comparison
with the conventional semiconductor chip cooling structures for
flip chip mounting which cool the semiconductor chip from its back
side or through the heat conduction channels of the circuit
board.
In the following, a concrete example of the semiconductor chip
cooling structure in accordance with the first embodiment of the
present invention will be described in detail referring to FIG.
2.
The size and the thickness of the semiconductor chip 1 is 3
mm.times.3 mm and 350 .mu.m, for example. On the peripheral part
(other than the center) of the surface of the semiconductor chip 1,
a plurality of surface electrodes are provided as input/output
terminals. The small-size circuit board 2 is a build-up circuit
board of a size of 23 mm.times.23 mm.times.1 mm (length, width,
thickness) having the center hole of 11 mm.times.11 mm, for
example. On the surface of the small-size circuit board 2, pads A
for the connection to the semiconductor chip 1 and pads B for the
connection to the large-size circuit board 3 are provided. The
large-size circuit board 3 is a glass-epoxy board of a size of 300
mm.times.300 mm.times.1.6 mm, for example. The large-size circuit
board 3 is provided with pads for the connection to the small-size
circuit board 2 on its surface and holes for passing the heat sink
fixation screws 7. The heat sink 4 is an aluminium heat sink of a
size of 43 mm.times.43 mm for example, having the convex part of a
size of 10 mm.times.10 mm.times.0.8 mm for example at the center of
its surface. The heat sink 4 is provided with holes for passing the
fixation screw 7 at its four corners and cooling fins on its back
side.
On each surface electrode of the semiconductor chip 1, an Au bump
is preliminarily formed. Meanwhile, on each pad A of the small-size
circuit board 2, a solder layer is preliminarily formed by means of
deposition. The semiconductor chip 1 is held by a holder (vacuum
chuck etc.), heated by the holder at a temperature higher than the
melting point of the solder, and pressed with a proper pressure
onto the small-size circuit board 2 which has been heated at a
temperature lower than the melting point of the solder, thereby the
solder on the pads A is melted and thereby the Au bumps of the
semiconductor chip 1 and the pads A of the small-size circuit board
2 are stuck together. When the semiconductor chip 1 is released by
the vacuum chuck, the solder hardens and thereby the connection
between the pads A and the Au bumps (i.e. the connection between
the small-size circuit board 2 and the semiconductor chip 1) is
completed. Subsequently, on each pads B of the small-size circuit
board 2, a solder ball is formed by applying solder paste on the
pad B, putting a Cu ball of a diameter of 450 .mu.m on the paste,
and executing reflow soldering. Meanwhile, on each pad of the
large-size circuit board 3, solder paste is preliminarily applied.
The small-size circuit board 2 to which the solder balls have been
formed and the large-size circuit board 3 are put together and
reflow soldering is executed, thereby the connection between the
small-size circuit board 2 and the large-size circuit board 3 is
completed. The solder balls (solder 6) are used in the
semiconductor chip cooling structure of FIG. 2 for providing
electrical connection and an appropriate space between the
small-size circuit board 2 and the large-size circuit board 3. At
this stage, the semiconductor chip 1, the small-size circuit board
2 and the large-size circuit board 3 have been connected together
structurally and electrically.
On the side of the heat sink 4, the thermal conduction material 5
(a thermal conduction compound, thermal conduction grease, a
thermal conduction rubber sheet, etc.) is preliminarily applied or
attached to the convex part. The heat sink 4 to which the thermal
conduction material 5 has been applied or attached is thereafter
fixed to the large-size circuit board 3 by means of the fixation
screws 7. Incidentally, the height of the convex part of the heat
sink 4 and the thickness of the thermal conduction material 5 are
determined and designed so that thermal connection between the
semiconductor chip 1 and the heat sink 4 can be maintained
enough.
As described above, in the semiconductor chip cooling structure in
accordance with the first embodiment of the present invention, the
fixation load for fixing the heat sink 4 to the large-size circuit
board 3 is held and supported by the small-size circuit board 2 and
the solder 6 which provides electrical connection between the
small-size circuit board 2 and the large-size circuit board 3,
therefore, the fixation load is not applied to the semiconductor
chip 1 at all. A load that is applied to the semiconductor chip 1
is determined by the relationship between the two thicknesses: the
first thickness of the convex part of the heat sink 4 and the
thermal conduction material 5 added together and the second
thickness of the small-size circuit board 2 and the chip connection
part (between the semiconductor chip 1 and the small-size circuit
board 2) added together, independently from the fixing load of the
heat sink 4. Therefore, the load applied to the semiconductor chip
1 can be controlled and reduced enough by designing the dimensions
of the parts appropriately, and thus damages to the semiconductor
chip 1 due to the fixation load can be eliminated. In the case
where the thermal conduction material 5 is implemented by an easily
deformed material or a pressure-absorbing material such as thermal
conduction grease, a thermal conduction rubber sheet, etc., the
effect of the fixation load to the semiconductor chip 1 can be
absorbed and eliminated without the need of determining a precise
thickness of the thermal conduction material 5.
Further, the surface of the semiconductor chip 1 is almost directly
connected to the convex part of the heat sink 4 via the thermal
conduction material 5, therefore, cooing of the semiconductor chip
1 can be executed more efficiently in comparison with the
conventional semiconductor chip cooling structures (for flip chip
mounting) which cool the semiconductor chip from its back side or
through the heat conduction channels of the circuit board.
FIG. 3 is a cross sectional view showing a semiconductor chip
cooling structure in accordance with a second embodiment of the
present invention. Referring to FIG. 3, the semiconductor chip
cooling structure -of the second embodiment includes a small-size
circuit board 2, a large-size circuit board 3, a heat sink 4,
solder 6, and fixation screws (bolts and nuts) 7, similarly to the
first embodiment. However, the semiconductor chip cooling structure
of the second embodiment is provided with N (N: 2, 3, . . . )
semiconductor chips 1 and N thermal conduction materials 5. In the
example of FIG. 3, the number N of the semiconductor chips 1 is
three. The small-size circuit board 2 is provided with N holes for
the N semiconductor chips 1, and the heat sink 4 is provided with
corresponding N convex parts.
The semiconductor chip cooling structure of the second embodiment
can be manufactured similarly to the case of the first embodiment,
as follows: First, the N semiconductor chips 1 are mounted on the
small-size circuit board 2 by connecting (by means of soldering
etc.) surface electrodes of the semiconductor chips 1 and pads of
the small-size circuit board 2 which have preliminarily been formed
so as to face the surface electrodes of the semiconductor chips 1.
The small-size circuit board 2 on which the N semiconductor chips 1
have been mounted is thereafter connected to the large-size circuit
board 3 by the solder 6. At this stage, the N semiconductor chips
1, the small-size circuit board 2 and the large-size circuit board
3 have been connected together as an electrically connected block.
Meanwhile, on the N convex parts of the heat sink 4, the N thermal
conduction materials 5 are previously applied or attached,
respectively. Thereafter, the heat sink 4 is attached to the
large-size circuit board 3 by means of the fixation screws 7
etc.
Incidentally, the height of the semiconductor chips 1 after being
mounted on the small-size circuit board 2 generally varies
slightly, and thereby small variation occurs in the distance
between each semiconductor chip 1 and a corresponding convex part
of the heat sink 4. However, the effects of the variation can be
absorbed and eliminated by selecting the material for the thermal
conduction material 5. Similarly to the case of the first
embodiment, if an easily deformed material or a pressure-absorbing
material (such as thermal conduction grease, a thermal conduction
rubber sheet, etc.) is employed as the thermal conduction material
5, the effects of the variation can easily be absorbed and
eliminated.
As described above, in the semiconductor chip cooling structure in
accordance with the second embodiment of the present invention, the
effects of the first embodiment can be obtained also in the case
where two or more semiconductor chips 1 are mounted on the
small-size circuit board 2.
As set forth hereinabove, in the semiconductor chip cooling
structure and a manufacturing method of a semiconductor chip
cooling structure in accordance with the present invention, a
semiconductor chip 1 is mounted on a small-size circuit board 2
having a hole, in flip-chip mounting. The small-size circuit board
2 is connected to a large-size circuit board 3 so that the
semiconductor chip 1 will be placed between the small-size circuit
board 2 and the large-size circuit board 3 and there will be a
clearance between the semiconductor chip 1 and the large-size
circuit board 3. A heat sink 4 is provided with a convex part for
being inserted into the hole of the small-size circuit board 2 to
be thermally connected to the surface of the semiconductor chip 1
through a thermal conduction material 5 which is sandwiched between
the convex part and the semiconductor chip 1. The heat sink 4 is
fixed to the large-size circuit board 3 by means of fixation means
such as the fixation screws 7 so that the semiconductor chip 1 and
the small-size circuit board 2 will be placed between the heat sink
4 and the large-size circuit board 3.
Therefore, the fixation load for fixing the heat sink 4 to the
large-size circuit board 3 is not applied to the semiconductor chip
1 at all and thereby damages to the semiconductor chip 1 due to the
fixation can be eliminated. The surface of the semiconductor chip 1
is almost directly connected to the convex part of the heat sink 4
via the thermal conduction material 5, therefore, the cooling of
the semiconductor chip 1 in flip-chip mounting can be executed with
high cooling efficiency. The present invention is also applied to
the cases where the number of the semiconductor chips 1 (i.e. the
number of the holes of the small-size circuit board 2, the number
of the convex parts of the heat sink 4, etc.) is N (N: 2, 3, 4, . .
. ).
While the present invention has been described with reference to
the particular illustrative embodiments, it is not to be restricted
by those embodiments but only by the appended claims. For example,
it is also possible to seal the structure between the small-size
circuit board 2 and the large-size circuit board 3 or between the
upper surface of the heat sink 4 and the large-size circuit board 3
by plastic or resin (epoxy resin etc.). It is to be appreciated
that those skilled in the art can change or modify the embodiments
without departing from the scope and spirit of the present
invention.
* * * * *